From: Alexey Tourbin <alexey.tourbin@gmail.com> To: devel@lists.altlinux.org Cc: Alexey Tourbin <alexey.tourbin@gmail.com> Subject: [devel] [PATCH] pack.c: downgrade XZ->LZMA automatically for small payloads Date: Sun, 20 Dec 2020 01:43:47 +0300 Message-ID: <20201219224347.230119-1-alexey.tourbin@gmail.com> (raw) Recent changes left downgradeLzmaLevel dysfunctional (because it does not recognize 'T'). In my view, the only advantage of XZ over LZMA is that XZ can can split input into blocks and compress them in parallel (resulting in a speed-up). Other advantages, such as a checksum, are immaterial for our purpose (because the package manager must verify the integrity of a package beforehand). Therefore, downgradeLzmaLevel will also downgrade XZ->LZMA automatically, for payloads smaller than 5*dictSize (the default blockSize being 3*dictSize, so that there are at least two blocks, the second block not too small). --- build/pack.c | 54 ++++++++++++++++++++++++++++++++++++++++------------ 1 file changed, 42 insertions(+), 12 deletions(-) diff --git a/build/pack.c b/build/pack.c index 23ad89e72..a779e7918 100644 --- a/build/pack.c +++ b/build/pack.c @@ -416,30 +416,60 @@ static uint64_t calcArchiveSize(TFI_t fi) // which is 8-64M. For smaller inputs, levels 7-9 are downgraded automatically. static void downgradeLzmaLevel(char *mode, uint64_t archiveSize) { -#define C(c) if (!(c)) return - C(mode[1] == '7' || mode[1] == '8' || mode[1] == '9'); - C(mode[2] == '.'); - C(mode[3] == 'l' || mode[3] == 'x'); - C(mode[4] == 'z'); + if (!(mode[1] >= '0' && mode[1] <= '9')) + return; + char *p = &mode[2]; + if (*p == 'T') { + do + p++; + while (*p >= '0' && *p <= '9'); + } + if (!(*p == '.' && (p[1] != 'l' || p[1] == 'x') && p[2] == 'z')) + return; #define S(m) ((m << 20) + (m << 10)) + // For small payloads, downgrade XZ->LZMA automatically. XZ only makes + // sense in multi-threaded mode (to speed up compression). The default + // block size in multi-threaded mode is three times the dictionary size. + // There has to be at least two blocks, the second block not too small, + // so we require at least five times the dictionary size. +#define T(m) ((m << 20) * 5) +#define ForceLzma memcpy(&mode[2], ".lzdio", 7) switch (mode[1]) { case '9': - if (archiveSize > S(32)) - break; + if (archiveSize < T(64)) ForceLzma; + if (archiveSize > S(32)) break; mode[1] = '8'; /*@fallthrough@*/ case '8': - if (archiveSize > S(16)) - break; + if (archiveSize < T(32)) ForceLzma; + if (archiveSize > S(16)) break; mode[1] = '7'; /*@fallthrough@*/ case '7': - if (archiveSize > S(8)) - break; + if (archiveSize < T(16)) ForceLzma; + if (archiveSize > S(8)) break; mode[1] = '6'; + /*@fallthrough@*/ + case '6': + case '5': + if (archiveSize < T(8)) ForceLzma; + break; + case '4': + case '3': + if (archiveSize < T(4)) ForceLzma; + break; + case '2': + if (archiveSize < T(2)) ForceLzma; + break; + case '1': + if (archiveSize < T(1)) ForceLzma; + break; + case 0: + // Dictionary size is 256K, but block size is 1M. + if (archiveSize < (7<<18)) ForceLzma; } -#undef C #undef S +#undef T } int writeRPM(Header *hdrp, const char *fileName, int type, -- 2.25.4
next reply other threads:[~2020-12-19 22:43 UTC|newest] Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-12-19 22:43 Alexey Tourbin [this message] 2020-12-20 0:38 ` Dmitry V. Levin 2020-12-20 0:49 ` Alexey Tourbin 2020-12-20 8:11 ` Dmitry V. Levin
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